1. Field of the Invention
This invention relates generally to disk drives, and more particularly to a magnetic recording disk drive that includes a system for canceling the adverse effects of shock and vibration disturbances.
2. Description of the Related Art
Magnetic recording hard disk drives (HDDs) use an actuator, typically a rotary voice-coil-motor (VCM) actuator, for positioning the read/write heads on the data tracks of the recording disks. The HDD has a servo control system that receives a position error signal (PES) from servo positioning information read by the heads from the data tracks and generates a VCM control signal to maintain the heads on track (track “following”) and move them to the desired track (track “seeking”) for reading and writing of data.
HDDs experience disturbance forces during normal operation that affect the positioning of the heads on the data tracks. These disturbances may arise internally, such as from motion of the VCM actuator. Because HDDs are used in a variety of environments they are also subject to a wide range of external disturbances, such as from shocks to the HDD frame, movement of other HDDs when multiple HDDs are mounted together in a disk array system, or movement of other computer components, such as compact disk (CD) drives.
HDDs may have one or more other types of sensors, such as accelerometers and rotational vibration sensors, that provide measurements of the disturbances. The output of these types of sensors is often used for suspending operation of the HDD until the disturbance has subsided. The measured signal from these types of sensors may also be input to a feedforward controller to create a control signal that compensates for the head's off-track motion caused by the disturbance. This feedforward method works effectively when the disturbance is purely rotational vibration, for which the gain and the phase of the transfer function from the sensor output and the PES is known and does not change. However, head position is affected not only by rotational vibration, but also by various kinds of linear and rotational internal and external disturbances for which the feedforward method is less effective.
Many HDD disturbances exhibit narrow-band frequency characteristics, often at a single frequency. To compensate for narrow-band disturbances, peak filters are often used in the HDD servo control system, if the frequency of the disturbance is known. However, the frequency of the disturbance may not be known and/or may vary with time. For example, a compact disk (CD) drive in a computer housing varies its rotational speed as it starts and stops and as it accesses different portions of the CD. The vibrations due to the rotation of the CD may disturb the operation of the computer's HDD. These disturbances are typically at a single frequency (and perhaps harmonics of the primary frequency) that varies with time. Since there is no communication between the CD drive and the HDD, the frequency of the disturbance is unknown to the HDD's servo control system.
In co-pending application Ser. No. 10/956,972, filed Sep. 30, 2004, by the same inventors as this application and assigned to the same assignee, an HDD is described that uses a plurality of peak filters coupled to the servo control system. The peak filters can be separately enabled or disabled, and may be variable to adjust the peak filter frequency up or down, so as to suppress disturbances over a relatively wide range of frequencies.
What is needed is a HDD that can identify the frequency of a disturbance and adjust the frequency of a peak filter as the disturbance frequency changes to quickly suppress the disturbance.